Relays are electromechanical switches operated by a flow of electricity in one circuit and controlling the flow of electricity in another circuit. A typical relay consists basically of an electromagnet with a soft iron bar, called an armature, held close to it. A movable contact is connected to the armature in such a way that the contact is held in its normal position by a spring. When the electromagnet is energized, it exerts a force on the armature that overcomes the pull of the spring and moves the contact so as to either complete or break a circuit. When the electromagnet is de-energized, the contact returns to its original position. Variations on this mechanism are possible: some relays have multiple contacts; some are encapsulated; some have built-in circuits that delay contact closure after actuation; some, as in early telephone circuits, advance through a series of positions step by step as they are energized and de-energized, and some relays are of latching type.
Coaxial RF switches are special types of electromechanical relays (or switches) wherein radio frequency (RF) signals are connected or disconnected between terminals in the switch. Typically a coaxial RF switch utilizes a pusher to push a conductor reed to make contact with a pair of coaxial conductor heads and connect the signal path between the two coaxial conductors. A common design uses a soft magnetic rocker under a pair of electromagnets to push the pusher for the switching action. The rocker-electromagnet assembly is typically symmetrical in construction in latching (bi-stable) type of switches. An additional restoring spring is added below one side of the rocker in a failsafe design to ensure the rocker returns to a predetermined state when the electromagnet is de-energized such that normally-on and normally-off arrangements can be achieved in the RF terminals. In such a failsafe design, strong magnetic attraction exists between the electromagnet and the rocker, therefore the strength of the restoring spring must be properly adjusted to achieve the desired normally-off contact configuration when the electromagnet is de-energized with reasonable power consumption during the “on” state when the electromagnet is energized. Such a balance is usually difficult and increased power consumption is necessary. The restoring spring also adds to the complexity in fabrication. Another failsafe-type of design uses a solenoid linear actuator to cause the conductor to connect and disconnect the RF terminals. Such a prior art solenoid linear actuator (FIG. 1) comprises a solenoid 20 which further comprises a coil 22 wound around a bobbin 21. Energizing solenoid 20 magnetizes soft magnetic core 10 and causes it to be attracted to soft magnetic bodies 18 and 19. The downward movement of soft magnetic core 10 pushes a push pin 15 and thus pusher 51 downward, causing conductor 51 to connect the RF terminals 60 and 61. A drawback in such a design is that soft magnetic body 14 is inserted inside of solenoid 20, and push pin 15 needs to be made of non-magnetic material and separated from soft magnetic core 10 which adds complexity in manufacturing and assembly. Another drawback is that the initial air gaps between the two ends of soft magnetic core 10 and soft magnetic bodies 18 and 19 are relatively large, causing unnecessarily large coil power consumption.
It is highly desirable to provide a solenoid linear actuator which is simple to manufacture and consumes low power during operations.
It is a purpose of the present invention to provide a new and improved solenoid linear actuator which is simple to manufacture and consumes low power during operations.